The present invention relates to fast switching thyristors in which the charge carrier lifetime is set to be short by means of recombination centers in order to shorten the turn-off time, and which have a zone structure including an emitter zone and a control base zone, with the emitter zone being penetrated by shorting channels which emanate from the control base zone. More particularly, the present invention relates to such a fast switching thyristor in which the charge carrier life-time is set to be homogeneous and low, corresponding to a desired firing resistance below the emitter zone with respect to the rise in the returning forward voltage across the thyristor after every turn-off process, and in which, in partial regions, the charge carrier lifetime is set to be low compared to the homogeneously set charge carrier lifetime. The invention further relates to a thyristor having a so-called amplifying gate as well as a method for producing such fast switching thyristors.
German Auslegeschrift (Published Patent Application) No. 1,489,087, published Sept. 3, 1970, discloses a semiconductor device, for example a so-called thyristor disc, having an improved frequency behavior and exhibiting the structural features mentioned in the first sentence except for the shorting channels in the emitter zone, as well as a method for producing such a semiconductor device.
In order to obtain improved frequency behavior, the turn-off time in the known device is likewise shortened by lowering the carrier lifetime in such a manner that within its volume or bulk through which current passes, there are disposed mutually separated regions or a grid-like interconnected region containing recombination centers in greater concentration than in the adjacent volume or bulk of the emitter zone and the control base zone. The increased number of recombination centers in this region or regions is formed by diffusion of, e.g., gold atoms, or by the influence, of radiation on the thyristor disc through a mask applied to one major surface of the element.
The regions of reduced carrier lifetime are to be effective only to a shallow depth below the n emitter zone and must, as is stated explicitly, not influence the two operationally effective pn-junctions between the p base zone and the n base zone and between the n base zone and the p emitter zone, respectively, i.e., at that depth no local reduction of the carrier lifetime is to be effected.
Moreover, German Offenlegungsschrift (application published without examination) No. 2,402,205, published Jan. 17th, 1974, discloses a method for reducing the turn-off time of a thyristor also having the above-mentioned structural features but again without shorting channels in the emitter zone. According to this method, the operational and ready-to-be connected thyristor element is subjected at one of its major surfaces to an orthogonally directed electron radiation of an energy greater than 1 MeV without masking. This reduces the charge carrier lifetime in the volume or bulk of the thyristor element spatially almost homogeneously and not, as explained above, in a localized distribution.
When an irradiation dosage in the order of magnitude of 10.sup.14 electrons/cm.sup.2 is employed, this results in a noticeable reduction of the turn-off time which, however, is connected with a marked increase in the forward voltage drop.
Finally, United States Patent Application Ser. No. 86,579, filed Oct. 19th, 1979 by Alois Sonntag et al, and assigned to the same assignee as the present application, discloses fast switching thyristors with shorted emitter structures, including those with amplifying gate structures, wherein a marked reduction of the turn-off time is realized, but without increasing the forward voltage drop, the firing current or the turn-on losses, by reducing the charge carrier lifetime in the thyristor in a localized distribution. In particular, the charge carrier lifetime beneath the emitter zone is set to be homogeneous and low, corresponding to a desired firing resistance beneath the emitter zone with respect to the rise in the returning forward voltage across the thyristor after every turn-off process, and in sharply delineated closed small regions arranged along the edge of the emitter zone facing the control electrode and intersected by the edge of the emitter zone, the charge carrier lifetime is set to be low compared to the homogeneous setting.